SANFORD, Fla. - The prosecution in the murder trial of George Zimmerman wrapped up its case Friday after a dramatic day of testimony with Travyon Martin's mother and brother saying the screams for help that can be heard in the background on a 911 call came from the 17-year-old.

Before the defense began its case, defense attorney Mark O'Mara argued Zimmerman should be acquitted, saying prosecutors hadn't proved their case.

"What is before the court is an enormous amount of information my client acted in self-defense," O'Mara told Judge Debra Nelson.

The defense’s request for acquittal was denied.

Testifying Friday was Dr. Shiping Bao, the medical examiner who performed the autopsy on Martin’s body.

Bao said he has changed his opinion about how long Martin was alive after being shot, and the effect of marijuana detected in Martin's body at the time of his death.

"It was my belief he was still alive, he was still in pain, he was still in suffering," said Bao.

The associate medical examiner said last November that he believed Martin was alive one to three minutes, but he testified Friday it was one to 10 minutes.

He also said Friday that marijuana could have affected Martin physically or mentally; he said the opposite last year.

The judge ruled before the trial that Martin's past marijuana use couldn't be introduced, and so the jury did not hear Bao's opinion about the drug's effect.

West and Bao talked over each other at several points, prompting the judge to tell everyone to speak one at a time.

During cross-examination, O'Mara suggested -- haltingly, in apparent recognition of the sensitivity of the questioning -- that Sybrina Fulton may have been influenced by others who listened to the 911 call, including relatives and her former husband.

O'Mara asked Fulton hypothetically whether she would have to accept that it was Zimmerman yelling for help if the screams did not come from her son.

"I heard my son screaming," Fulton answered firmly.

The defense attorney also asked Fulton whether she hoped Martin didn't do anything that led to his death.

"I would hope for this to never have happened and he would still be here," she said.

Fulton was followed on the stand by her son, Jahvaris Fulton, Martin's 23-year-old half-brother, who also testified the cries came from Martin.

But O'Mara asked him why last year he had told a reporter that he wasn't sure if the voice belonged to Martin. Jahvaris Fulton, in explaining his comment to the reporter, told O'Mara he was "shocked" when he heard it.

"I didn't want to believe it was him," Jahvaris Fulton said.

O'Mara asked to play the television interview for jurors, but Nelson denied his request for the time being.

Jahvaris Fulton's testimony was broken up by efforts to unlock the evidence room adjacent to the courtroom. Unable to open it, court officials called a locksmith with a drill to help them out.